1. Field of the Invention
The present invention relates to an apparatus for and method of manufacturing a semiconductor device. More particularly, the invention relates to an apparatus for and method of etching.
2. Description of the Background Art
With recent increase in scale of integration of semiconductor devices, high-finishing-accuracy micro-etching techniques have been increasingly important. For instance, a plasma etching technique is known as a process suitable for micromachining, and is often used in the step of trench formation for forming finer interconnect lines on a semiconductor substrate.
FIGS. 8A and 8B show the steps of forming buried interconnect lines in a background art method of manufacturing a semiconductor device. The background art method of manufacturing the semiconductor device will be described with reference to FIGS. 8A and 8B. First, a to-be-etched film 101 in which buried interconnect lines are to be formed is formed on a semiconductor device 100. Then, a photoresist film is formed on the film 101 and is selectively removed in portions to be trenched, to form a resist pattern 102. Using the resist pattern 102 as a mask, etching is performed on the film 101 to form trenches 103, as shown in FIG. 8A.
Then, the resist pattern 102 is removed. Barrier metal 104, e.g. TaN, is provided in the trenches 103, and the trenches 103 are filled with a wiring material, e.g. Cu. This forms buried interconnect lines 105, as shown in FIG. 8B.
Thus, the thickness of the buried interconnect lines 105 is determined by the depth of the trenches 103 formed in the film 101. Also, the thickness of the buried interconnect lines 105 greatly influences the resistance thereof. Therefore, variations in the depth of the trenches 103 result in variations in the resistance of the buried interconnect lines 105 from a design value to become a factor responsible for the decrease in semiconductor device manufacturing yield.
In an etching process, it has been relatively easily carried out, for example, to form a second film having an etch selectivity to the to-be-etched film under the to-be-etched film and to use the second film as a stopper to control an etch depth. In this case, the to-be-etched film in an etching region is completely removed. In other words, the etch depth is equivalent to the thickness of the to-be-etched film.
However, the above-mentioned trench formation process, in which the depth of the trenches in the to-be-etched film is less than the thickness of the to-be-etched film, is required to stop the etching without using the stopper, i.e., to etch the to-be-etched film to a desired depth. It is difficult for the background art etching method to precisely control the etch depth.
To overcome the difficulties, an attempt can be contemplated to monitor the depth of the trenches being formed using a film thickness measuring device of an optical interference type during the etching. However, it is in many cases difficult to place the film thickness measuring device in an etching chamber of an etching apparatus from a structural viewpoint. Additionally, even if the film thickness measuring device can be placed in the etching chamber, the monitoring in a plasma is difficult and impractical in the above-mentioned plasma etching process.
It is an object of the present invention to provide a method of and apparatus for etching capable of suppressing variations in etch depth.
A first aspect of the present invention is intended for an etching apparatus having an etching chamber for etching a film formed on a surface of a wafer, and at least one of a buffer chamber and an orienter chamber for establishing an orientation of the wafer. According to the present invention, the etching apparatus includes: an etching device for performing the etching; and an etch depth measuring device for measuring an etch depth resulting from the etching.
The etching device is provided in the etching chamber. The etch depth measuring device is provided in one of the buffer chamber and the orienter chamber. The etching device additionally performs the etching if the etch depth measured by the etch depth measuring device is less than a predetermined value.
The etching apparatus according to the present invention can suppress variations in etch depth, thereby to contribute to improvements in semiconductor device manufacturing yield. Additionally, since the orienter chamber and the transport buffer chamber are typically provided in a conventional common etching apparatus, there is no need to provide a new space for placement of a film thickness measuring device.
Preferably, the etching apparatus further includes a setting device for setting a value of a parameter associated with the etching, wherein the parameter includes an etch depth setting for the etching and an actual etch rate estimate.
The etching apparatus according to the prevent invention can precisely determine etch time for additional etching to suppress the variations in etch depth.
A second aspect of the present invention is intended for a method of etching a film formed on a surface of a wafer to a predetermined depth less than the thickness of the film. According to the present invention, the method includes the following steps (a) to (c).
The step (a) etches the film formed on a surface of a first wafer for first etch time. The step (b) measures a first etch depth, the first etch depth being an actual etch depth resulting from the etching in the step (a). The step (c) additionally performs the etching for additional etch time if the first etch depth is less than a predetermined value. The first etch time is calculated from an etch depth setting for the etching in the step (a) and a first etch rate, the first etch rate being an actual etch rate estimate. The additional etch time is calculated from the etch depth setting, the first etch depth and an additional etch rate, the additional etch rate being an actual etch rate estimate for the etching in the step (c).
In the method according to the present invention, the step (c) corrects variations in etch depth resulting from the etching in the step (a), to consequently suppress the variations in etch depth. This contributes to improvements in semiconductor device manufacturing yield.
Preferably, in the method of the present invention, the additional etch rate is the first etch rate.
In the method according to the present invention, the step (c) corrects the variations in etch depth resulting from the etching in the step (a) to consequently suppress the variations in etch depth.
Preferably, in the method of the present invention, the additional etch rate Radd is calculated in accordance with the equation Radd=D1act/T1 where D1act is the first etch depth, and T1 is the first etch time.
The method according to the present invention can precisely determine the additional etch rate Radd. Therefore, the step (c) precisely corrects the variations in etch depth resulting from the etching in the step (a) to consequently suppress the variations in etch depth.
Preferably, in the method of the present invention, the first wafer further includes an upper-layer film on the film. The method further includes the step of (d) etching the upper-layer film, the step (d) being performed before the step (a). The additional etch rate Radd is calculated in accordance with the equation Radd=(D1actxe2x88x92Dv)/T1 where D1act is the first etch depth, Dv is an overetch depth in an upper surface of the film in the step (d), and T1 is the first etch time.
The method according to the present invention can correct the influence of the amount of overetching to determine the additional etch rate Radd. Therefore, the step (c) precisely corrects the variations in etch depth resulting from the etching in the step (a) to consequently suppress the variations in etch depth.
Preferably, the method of the present invention further includes the following steps (e) and (f). The step (e) performs the etching on the film formed on a surface of a second wafer for second etch time. The step (f) measures a second etch depth, the second etch depth being an actual etch depth resulting from the etching in the step (e). The additional etch rate Radd is calculated in accordance with the equation Radd=D2act/T2 where D2act is the second etch depth, and T2 is the second etch time.
The method according to the present invention can reduce the influence of a change in etch rate depending on the number of processed wafers in an etching apparatus to precisely determine the additional etch rate Radd. Therefore, the step (c) precisely corrects the variations in etch depth resulting from the etching in the step (a) to consequently suppress the variations in etch depth.
Preferably, the method of present invention further includes the step of (g) approximating a relationship between an etch rate and etch time of the film using a polynomial, wherein the additional etch rate is calculated based on the polynomial.
The method according to the present invention can precisely determine the additional etch rate if the relation between the etch rate and the etch time is not linear. Therefore, the step (c) precisely corrects the variations in etch depth resulting from the etching in the step (a) to consequently suppress the variations in etch depth.
Preferably, the method of present invention further includes the following steps (h) and (i). The step (h) performs the etching on the film formed on a surface of a third wafer for third etch time, the step (h) being performed before the step (a). The step (i) measures a third etch depth, the third etch depth being an actual etch depth resulting from the etching in the step (h). The first etch rate R1 is calculated in accordance with the equation R1=D3act/T3 where D3act is the third etch depth, and T3 is the third etch time.
The method according to the present invention improves the accuracy of the etch depth resulting from the etching in step (a). This achieves the reduction in the number of wafers which need the additional etching process in the etching apparatus according to the present invention to contribute to improvements in semiconductor device manufacturing efficiency.
A third aspect of the present invention is intended for a method of etching a film formed on surfaces of a plurality of wafers to a predetermined depth less than the thickness of the film. According to the present invention, the method includes the following steps (a) to (c).
The step (a) performs the etching on the film formed on a surface of a first wafer for first etch time. The step (b) measures an actual etch depth resulting from the etching in the step (a). The step (c) performs the etching on the film formed on a surface of a second wafer for second etch time, the step (c) being performed after the step (b). The second etch time T2 is calculated in accordance with the equation T2=Dset/(Dact/T1) where Dset is an etch depth setting for the etching, Dact is the actual etch depth measured in the step (b), and Ti is the first etch time.
The method according to the present invention improves the accuracy of the etch depth resulting from the etching in step (c). This contributes to the improvements in semiconductor device manufacturing efficiency.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.